Implant receivers and connectors with grip grooves for rod fixation

ABSTRACT

Implants with grip grooves are disclosed herein. In some embodiments, an implant includes a rod-receiving recess defining a rod axis where an inner surface of the rod-receiving recess defines two grip grooves extending parallel to each other and the rod axis. Each grip groove defines two edges where the grip groove intersects the inner surface, the four edges of the two grip grooves together defining a circular radius about the rod axis. The implant includes a retaining member configured to move with respect to the body to apply a force against a rod that is perpendicular to the rod axis, the force engaging the rod against the four edges of the grip grooves, where the engagement of the four edges of the grip grooves against the rod restrains rotational movement of the rod about the rod axis.

FIELD

Implant receivers and connectors with grip grooves for improved rodfixation are disclosed herein.

BACKGROUND

Fixation systems can be used in orthopedic surgery to maintain a desiredspatial relationship between multiple bones or bone fragments. Forexample, various conditions of the spine, such as fractures,deformities, and degenerative disorders, can be treated by attaching aspinal fixation system to one or more vertebrae. Such systems typicallyinclude a spinal fixation element, such as a rigid or flexible rod orplate that is coupled to the vertebrae by attaching the element tovarious anchoring devices, such as screws, hooks, or wires. Onceinstalled, the fixation system holds the vertebrae in a desired positionuntil healing or spinal fusion can occur, or for some other period oftime.

In screw and rod spinal fixation constructs, stability of the implantedconstruct is crucial in allowing the body to accomplish bony fusionthrough the operative levels. Instability of, or motion within animplanted construct can result in a pseudoarthrosis, a “non-union” wherenew bone formation fails to take over loads experienced by the screw androd construct. Where there is too much motion allowed betweeninstrumented vertebrae, growth activity is hindered; new bone cannotfuse between two bodies that are constantly moving relative to oneanother. To solve this problem and provide stable fixation, polyaxialscrew-heads, rod to rod, and screw-head to rod connectors all need tohold securely to the rod. These implants must resist motion relative tothe longitudinal rods in the construct; this includes the rod sliding,rotating, or pulling away from the connector or bone screw.

There are many instances in which it may be desirable to connectmultiple implants to each other. For example, some revision surgeriesinvolve extending a previously-installed construct to additionalvertebral levels by coupling a newly-installed spinal rod to apreviously-installed rod. In addition, with vertebral implants orconstructs fixated in the cervical and thoracic regions of the spine, arod-to-rod connector can be used to bridge the transition between theconstructs or implants in the cervical and thoracic regions. In thisexample, and in other transition regions, torsional slip between theimplants on the rod or rods connecting them to each other is a seriousrisk, which can be caused by routine and repetitive movements, forexample the patient twisting their head. By way of further example,aspects of the patient's anatomy, the surgical technique used, or thedesired correction may require that multiple spinal rods be connected toone another. As yet another example, coupling multiple rods to oneanother can improve the overall strength and stability of an implantedconstruct.

There can be various difficulties associated with connecting multipleimplants to each other. The available space for the implanted constructcan often be very limited, particularly in the cervical area of thespine. Also, manipulating and handling these relatively small implantsin the surgical wound may be challenging or cumbersome for the surgeon.There is a continual need for improved implant connectors and relatedmethods.

SUMMARY

Certain examples of the present disclosure include an implant with abody having a rod-receiving recess, where the body has first and secondsides defining openings to the rod-receiving recess and therod-receiving recess defines a central longitudinal rod axis extendingbetween the openings of the first and second sides. At least a portionof the rod-receiving recess can be formed by an inner surface of theimplant, with the inner surface defining two grip grooves extendingparallel to each other and the central longitudinal rod axis. Each gripgroove defines two edges where the grip groove intersects the innersurface, the four edges of the two grip grooves together defining acircular radius about the central longitudinal rod axis. The implantalso includes a retaining member configured to move with respect to thebody, exert a force against a rod in the rod-receiving recess that canbe perpendicular to the central longitudinal rod axis, and engage therod against the four edges of the two grip grooves. Additionally,engagement of the four edges of the grip grooves against the rod canrestrain rotational movement of the rod about the central longitudinalrod axis.

In some examples, the rod-receiving recess defines a gap between the twogrip grooves sized and positioned to allow the force against the rod inthe rod-receiving recess to permit deflection of one or both of theedges and the rod where the edges engage the rod, the deflection causingmovement of the rod into the gap. The inner surface of the rod-receivingrecess between the two grip grooves can be positioned a distance awayfrom the central longitudinal rod axis that is larger than a radius ofthe rod.

In some examples, the implant includes a compression member disposed ina cavity formed in the body, with the compression member having an innersurface defining at least a portion of the rod-receiving recess, with aninner surface of the compression member having the two grip groovesformed therein. In some examples, the grip grooves extend along anentire length of the inner surface of the rod-receiving recess in thedirection of the central longitudinal rod axis. In some examples, thegrip grooves are positioned opposite the retaining member with respectto the central longitudinal rod axis.

The rod-receiving recess can define an open end sized to accept the rodand a closed end sized to contact the rod, where the grip grooves arearranged symmetrically about an axis extending from the open end to theclosed end. The body of the implant can define the inner surface formingthe rod-receiving recess. In some examples, the intersection between thegrip grooves and the inner surface defines sharp edges.

The inner surface can define a groove intersecting at least one gripgroove, the intersection of the groove segmenting the edges of the atleast one grip groove and defining four corners for resistingtranslation of the rod along the central longitudinal rod axis when therod is engaged with the edges. In some examples, the groove intersectingat least one grip groove is oriented perpendicular to the grip grooves.

The grip grooves can be formed by protrusions extending from the innersurface. In some examples, at least one grip groove defines an innersurface having formed therein one or more protrusions, the one or moreprotrusions extending to edges arranged to contact the rod when the rodis engaged with the edges of the grip grooves.

In some examples, the implant includes a connector and the rod-receivingrecess is a first rod-receiving recces, the body defining a secondrod-receiving recesses, with one or both of the first and secondrod-receiving recesses having the two grip grooves. The body hasproximal and distal ends that define a proximal-distal axis extendingtherebetween, with the retaining member slidably disposed within atunnel formed in the body and configured to translate with respect tothe body along a rod pusher axis.

In some examples, the second rod-receiving recess is defined by a pairof spaced apart arms of the body. The first rod-receiving recess can beopen in a distal direction and the second rod-receiving recess can beopen in a proximal direction. The rod pusher axis can be substantiallyperpendicular to the proximal-distal axis. In some examples, the implantfurther includes a set screw threadably received in the body to lock afirst rod within the first rod-receiving recess and to lock a second rodwithin the second rod-receiving recess.

The implant can include a bone anchor assembly, with the body having areceiver member of the bone anchor assembly and the retaining memberhaving a set screw or locking element.

Another example of the present disclosure is an implant having a bodyhaving a rod-receiving recess, a grip insert configured to be positionedin an open end of the receiving recess, and a retaining memberconfigured to move with respect to the body. The body has first andsecond sides defining openings to the rod-receiving recess and therod-receiving recess defines a central longitudinal rod axis extendingbetween the openings of the first and second sides. The grip insert hasan inner surface for contacting a rod disposed in the rod-receivingrecess, with the inner surface defining two grip grooves extendingparallel to each other and the central longitudinal rod axis, where eachgrip groove defines two edges where the grip groove intersects the innersurface and the four edges of the two grip grooves together defining acircular radius about the central longitudinal rod axis. The retainingmember can be configured to exert a force against a rod in therod-receiving recess and engage the four edges of the grip against therod, where the engagement of the four edges of the grip grooves againstthe rod serves to restrain rotational movement of the rod about thecentral longitudinal rod axis.

Any of the features or variations described above can be applied to anyparticular example of the present disclosure in a number of differentcombinations. The absence of explicit recitation of any particularcombination is due solely to the avoidance of repetition in thissummary.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a prior art bone anchor assembly;

FIG. 1B is an exploded view of the bone anchor assembly of FIG. 1A;

FIG. 1C is a top view of the bone anchor assembly of FIG. 1A;

FIG. 1D is a cross-sectional view of the bone anchor assembly of FIG.1A;

FIG. 2A is a perspective view of a prior art connector;

FIG. 2B is an exploded perspective view of the connector of FIG. 2Ashown with first and second spinal rods;

FIG. 2C is a sectional side view of the connector of FIG. 2A in a firstconfiguration;

FIG. 2D is a sectional top view of the connector of FIG. 2A in the firstconfiguration;

FIG. 2E is a sectional side view of the connector of FIG. 2A in a secondconfiguration;

FIG. 2F is a sectional top view of the connector of FIG. 2A in thesecond configuration;

FIG. 2G is a sectional side view of the connector of FIG. 2A in a thirdconfiguration;

FIG. 2H is a sectional top view of the connector of FIG. 2A in the thirdconfiguration;

FIG. 2I is a side view of the connector of FIG. 2A coupled to first andsecond spinal rods;

FIG. 2J is a perspective view of the connector of FIG. 2A shown with asaddle;

FIG. 2K is an exploded perspective view of the connector and saddle ofFIG. 2J shown with first and second spinal rods;

FIG. 2L is a sectional side view of the connector and saddle of FIG. 2Jcoupled to first and second spinal rods;

FIG. 3A is a cross-sectional view of one embodiment of a connector witha rod recess having two grip grooves;

FIG. 3B is a cross-sectional view of the rod-receiving recess of theconnector of FIG. 3A;

FIG. 3C is a cross-sectional view of the grip grooves of therod-receiving recess of the connector of FIG. 3A;

FIG. 4A is a cross-sectional view of a prior art rod-receiving recess;

FIG. 4B is a cross-sectional view of one embodiment of a rod-receivingrecess having v-shaped grip grooves;

FIG. 4C is a cross-sectional view of the rod-receiving recess of FIG. 4Bshowing a comparison of the position of a rod with and without the gripgrooves;

FIG. 4D is a perspective view of a rod showing lines of contact made bythe edges of the two grip grooves of FIG. 4B when the rod is positionedin the rod-receiving recess of FIG. 4B;

FIG. 4E is a perspective view of a surface of one embodiment of arod-receiving recess with a segmented grip groove;

FIG. 4F is a top-down view of the segmented grip groove of FIG. 4E;

FIG. 4G is an schematic illustration of the contact points on a rodengaged with the segmented grip groove of FIG. 4E;

FIG. 4H is a perspective of a surface of a rod showing lines of contactmade by the edges of the two segmented grip grooves of FIG. 4E when therod is positioned in the rod-receiving recess of FIG. 4E;

FIG. 5A is a cross-sectional view of one embodiment of a rod-receivingrecess having grip grooves of an alternative shape;

FIG. 5B is a cross-sectional view of one embodiment of a rod-receivingrecess having grip grooves formed by protrusions;

FIG. 6A is a cross-sectional view of one embodiment of a rod-receivingrecess and a rod pusher having grip grooves;

FIG. 6B is a cross-sectional view of an alternate embodiment of arod-receiving recess and with a rod pusher having grip grooves;

FIG. 6C is a cross-sectional view of one embodiment of a rod-receivingrecess and rod pusher both having grip grooves;

FIG. 7A is a cross-sectional view of one embodiment of a single gripgroove having an internal protrusion arranged to contact the rod in thegrip groove perpendicular to the edges of the grip groove;

FIG. 7B is a top-down view of the grip groove of FIG. 7A showing theperpendicular edges of the internal protrusion;

FIG. 7C is a cross-sectional view of the grip groove of FIG. 7A showingthe edges of the internal protrusions contacting the rod when the rod isengaged with the grip groove;

FIG. 7D is a perspective view of a rod showing lines of contact made bythe edges of the two grip grooves of FIG. 7A with internal protrusions;

FIGS. 7E and 7F are cross-sectional views of embodiments of a singlegrip groove having an internal protrusion with two differentconfigurations;

FIG. 8A is a cross-sectional view of a prior art rod-receiving recess;

FIG. 8B is a cross-sectional view of one embodiment of a rod-receivingrecess with two grip grooves;

FIG. 8C is a cross-sectional view of one embodiment of a rod-receivingrecess and a rod engagement element with two grip grooves;

FIG. 8D is a cross-sectional view of an alternative embodiment of arod-receiving recess and a rod engagement element with two grip grooves;

FIG. 9 is a perspective view of one embodiment of a receiving memberhaving a rod-receiving recess with two grip grooves;

FIG. 10 is a perspective view of one embodiment of a receiving memberhaving a rod-receiving recess with two circumferential grooves;

FIGS. 11A and 11B are perspective views of one embodiment of a receivingmember having a rod-receiving recess with two segmented grip groovesformed by the intersection of two grip grooves and two circumferentialgrooves;

FIG. 12 is a perspective view of one embodiment of a receiving memberhaving a rod-receiving recess with two grip grooves having multipleinternal protrusions;

FIG. 13 is cross-sectional view of one embodiment of a connector with arod-receiving recess having two grip grooves;

FIG. 14 is cross-sectional view of one embodiment of a bone anchorassembly with a compression member forming a rod-receiving recess and arod engagement element with two grip grooves; and

FIG. 15 is a perspective view of a human spine with a fixation systemattached thereto.

DETAILED DESCRIPTION

Implants with grip grooves and related methods are disclosed herein. Theimplants can include connectors and receiver members of bone anchorassemblies. In some examples, a connector can include a low-profileportion to facilitate use of the connector in surgical applicationswhere space is limited. In some embodiments, a connector can include abiased rod-pusher to allow the connector to “snap” onto a rod and/or to“drag” against the rod, e.g., for provisional positioning of theconnector prior to locking.

Certain aspects of the present disclosure provide for increasedtorsional gripping capacity of an implant on a rod. One examplepresented is a rod-to-rod connector, but the feature may be applied tovarious spinal implants such as screw heads of bone anchor assemblies.Aspects of the present disclosure include single or multiplelongitudinal grooves cut in the rod slot of an implant that add extralines of contact between the connector and the rod. In operation, whenlocked, a very small portion of the cross-sectional rod perimeter iswedged into the groove, causing both edges where the groove cut beginsto press into the rod. Even if the rod tangency is not perfectly locatedrelative to this groove, the groove provides an edge, rather than a flatface, to grind against the rod and prevent further rotation shouldrotation begin to occur from forces exerted upon the rod or connector.This micro-shearing of the material is the principle of increasingtorsional gripping capacity.

Alternatively, these grip grooves can be on the surface of the rodinstead of the connector, screw head, or receiving implant. In addition,the semi-circular grip grooves can be other geometries, such asrectangular, right angle or other angles, trapezoidal, etc.

A variation of the grip groove to increase the axial slip (longitudinalrod sliding) gripping capacity is to have the grooves in acircumferential orientation relative to the rod. The longitudinal andthe circumferential grip grooves can also be combined to increasetorsional and axial resistance. The resulting features may resemble pegsor corners.

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the structure, function,manufacture, and use of the devices and methods disclosed herein. One ormore examples of these embodiments are illustrated in the accompanyingdrawings. Those skilled in the art will understand that the devices andmethods specifically described herein and illustrated in theaccompanying drawings are non-limiting exemplary embodiments. Thefeatures illustrated or described in connection with one exemplaryembodiment may be combined with the features of other embodiments.

FIGS. 1A-1D illustrate a prior art bone anchor assembly 10 including abone anchor 12, a receiver member 14 for receiving a spinal fixationelement, such as a spinal rod 22, to be coupled to the bone anchor 12,and a closure mechanism 16 to capture a spinal fixation element withinthe receiver member 14 and fix the spinal fixation element with respectto the receiver member 14. The bone anchor 12 includes a proximal head18 and a distal shaft 20 configured to engage bone. The receiver member14 has a proximal end 26 having a pair of spaced apart arms 28A, 28Bdefining a recess 30 therebetween and a distal end 32 having an innersurface 35 for polyaxially seating the proximal head 18 of the boneanchor 12 and distal end surface 34 defining an opening through which atleast a portion of the bone anchor 12 extends. The closure mechanism 16can be positionable between and can engage the arms 28A, 28B to capturea spinal fixation element, e.g., a spinal rod 22, within the receivermember 14 and fix the spinal fixation element with respect to thereceiver member 14.

The proximal head 18 of the bone anchor 12 is generally in the shape ofa truncated sphere having a planar proximal surface 36 and anapproximately spherically-shaped distal surface 38. The illustrated boneanchor assembly is a polyaxial bone anchor designed for posteriorimplantation in the pedicle or lateral mass of a vertebra. The proximalhead 18 of the bone anchor 12 engages the distal end 32 of the receivermember 14 in a ball and socket like arrangement in which the proximalhead 18 the distal shaft 20 can pivot relative to the receiver member14. The distal surface 38 of the proximal head 18 of the bone anchor 12and a mating surface within the distal end 32 of the receiver member 14can have any shape that facilitates this arrangement, including, forexample, spherical (as illustrated), toroidal, conical, frustoconical,and any combinations of these shapes.

The distal shaft 20 of the bone anchor 12 can be configured to engagebone and, in the illustrated embodiment, includes an external boneengaging thread 40. The thread form for the distal shaft 20, includingthe number of threads, the pitch, the major and minor diameters, and thethread shape, can be selected to facilitate connection with bone.Exemplary thread forms are disclosed in U.S. Patent ApplicationPublication No. 2011/0288599, filed on May 18, 2011, and in U.S.Provisional Patent Application Ser. No. 61/527,389, filed Aug. 25, 2011,both of which are incorporated herein by reference. The distal shaft 20can also include other structures for engaging bone, including a hook.The distal shaft 20 of the bone anchor 12 can be cannulated, having acentral passage or cannula extending the length of the bone anchor tofacilitate delivery of the bone anchor over a guide wire in, forexample, minimally-invasive procedures. Other components of the boneanchor assembly, including, for example, the closure member 16, thereceiver member 14, and the compression member 60 (discussed below) canbe cannulated or otherwise have an opening to permit delivery over aguide wire or to permit the insertion of a driver instrument tomanipulate the bone anchor. The distal shaft 20 can also include one ormore sidewall openings or fenestrations that communicate with thecannula to permit bone in-growth or to permit the dispensing of bonecement or other materials through the bone anchor 12. The sidewallopenings can extend radially from the cannula through the sidewall ofthe distal shaft 20. Exemplary systems for delivering bone cement to thebone anchor assembly 10 and alternative bone anchor configurations forfacilitating cement delivery are described in U.S. Patent ApplicationPublication No. 2010/0114174, filed on Oct. 29, 2009, which is herebyincorporated herein by reference. The distal shaft 20 of the bone anchor12 can also be coated with materials to permit bone growth, such as, forexample, hydroxyl apatite, and the bone anchor assembly 10 can be coatedpartially or entirely with anti-infective materials, such as, forexample, triclosan.

The proximal end 26 of the receiver member 14 includes a pair of spacedapart arms 28A, 28B defining a U-shaped recess 30 therebetween forreceiving a spinal fixation element, e.g., a spinal rod 22. Each of thearms 28A, 28B can extend from the distal end 32 of the receiver member14 to a free end. The outer surfaces of each of the arms 28A, 28B caninclude a feature, such as a recess, dimple, notch, projection, or thelike, to facilitate connection of the receiver member 14 to instruments.For example, the outer surface of each arm 28A, 28B can include anarcuate groove at the respective free end of the arms. Such grooves aredescribed in more detail in U.S. Pat. No. 7,179,261, issued on Feb. 20,2007, which is hereby incorporated herein by reference. At least aportion of the proximal end surface 48 of the receiver member 12 definesa plane Y. The receiver member 14 has a central longitudinal axis L.

The distal end 32 of the receiver member 14 includes a distal endsurface 34 which is generally annular in shape defining a circularopening through which at least a portion of the bone anchor 12 extends.For example, the distal shaft 20 of the bone anchor 12 can extendthrough the opening. At least a portion of the distal end surface 34defines a plane X.

The bone anchor 12 can be selectively fixed relative to the receivermember 14. Prior to fixation, the bone anchor 12 is movable relative tothe receiver member 14 within a cone of angulation generally defined bythe geometry of the distal end 32 of the receiver member and theproximal head 18 of the bone anchor 12. The illustrated bone anchor is afavored-angle polyaxial screw in which the cone of angulation is biasedin one direction. In this manner, the bone anchor 12 is movable relativeto the receiver member 14 in at least a first direction, indicated byarrow A in FIG. 1D, at a first angle C relative to the centrallongitudinal axis L of the receiver member 14. The bone anchor 12 isalso movable in at least a second direction, indicated by arrow B inFIG. 1D, at a second angle D relative to the longitudinal axis L. Thefirst angle C is greater than the second angle D and, thus, the shaft 20of the bone anchor 12 is movable more in the direction indicated byarrow A than in the direction indicated by arrow B. The distal shaft 20of the bone anchor 12 defines a neutral axis 48 with respect to thereceiver member 14. The neutral axis 48 can be perpendicular to theplane X defined by the distal end surface 34 and intersects the centerpoint of the opening in the distal end surface 34 through which thedistal shaft 20 of the bone anchor 12 extends. The neutral axis 48 canbe oriented at an angle to the central longitudinal axis L of thereceiver member 14. The plane Y defined by at least a portion of theproximal end surface 48 of the receiver member 14 intersects the plane Xdefined by at least a portion of the distal end surface 34 of thereceiver member 12. The proximal end 26 of the receiver member 14 caninclude a proximal first bore 50 coaxial with a first centrallongitudinal axis N (which is coincident with longitudinal axis L) and adistal second bore 52 coaxial with a second central longitudinal axis M(which is coincident with the neutral axis 48) and the first centrallongitudinal axis N and second central longitudinal axis M can intersectone another. The angle between the plane X and the plane Y and the anglebetween the axis L and the axis M can be selected to provide the desireddegree of biased angulation. Examples of favored angled polyaxial screwsare described in more detail in U.S. Pat. No. 6,974,460, issued on Dec.13, 2005, and in U.S. Pat. No. 6,736,820, issued on May 18, 2004, bothof which are hereby incorporated herein by reference. Alternatively, thebone anchor assembly can be a conventional (non-biased) polyaxial screwin which the bone anchor pivots in the same amount in every directionand has a neutral axis that is coincident with the central longitudinalaxis L of the receiver member.

The spinal fixation element, e.g., the spinal rod 22, can eitherdirectly contact the proximal head 18 of the bone anchor 12 or cancontact an intermediate element, e.g., a compression member 60. Thecompression member 60 can be positioned within the receiver member 14and interposed between the spinal rod 22 and the proximal head 18 of thebone anchor 12 to compress the distal outer surface 38 of the proximalhead 18 into direct, fixed engagement with the distal inner surface ofthe receiver member 14. A proximal portion of the compression member 60can include a pair of spaced apart arms 62A and 62B defining a U-shapedseat 64 for receiving the spinal rod 22. A distal portion of thecompression member 60 can include a sidewall having an inner cylindricalsurface 67 that is connected to an outer cylindrical surface 68 by adistal-facing surface 66,

At least a portion of the distal surface 66 of the compression member 60can be shaped as a negative of the proximal portion 18 of the boneanchor 20, against which the distal surface 66 abuts when thecompression member 60 is fully inserted into the receiver member 14.Thus, when the shaft 20 of the bone anchor 12 is oriented along thelongitudinal axis L, the contact area between the distal surface 66 ofthe compression member 60 and the proximal head 18 is maximized. Wherethe angle of the shaft 20 with respect to the longitudinal axis L is notzero, however, the contact area between the distal surface 66 of thecompression member 60 and the head 18 can be reduced, thus increasing arisk of slippage of the bone anchor 12 with respect to the receivermember 14.

As best seen in FIG. 1B, the compression member 60 is configured toslide freely along the longitudinal axis L within the recess 30 of thereceiver member 14. To secure the compression member 60 within thereceiver member 14, the compression member 60 can be configured to matewith the receiver member, for example by mechanically deforming aportion of the compression member 60 against the receiver member 14. Inthe illustrated embodiment, opposing bores formed in the arms 62A, 62Bof the compression member 60 are aligned with bores formed in the arms62A, 62B of the receiver member 14, such that opposing pins can beinserted through the passageways defined by the bores to compress or“swage” the compression member 60 against the receiver member 14. Theswaging process can prevent subsequent removal of the compression member60 from the receiver member 14.

The proximal end 26 of the receiver member 14 can be configured toreceive a closure mechanism 16 positionable between and engaging thearms 28A, 28B of the receiver member 14. The closure mechanism 16 can beconfigured to capture a spinal fixation element, e.g., a spinal rod 22,within the receiver member 14, to fix the spinal rod 22 relative to thereceiver member 14, and to fix the bone anchor 12 relative to thereceiver member 14. The closure mechanism 16 can be a single set screwhaving an outer thread for engaging an inner thread 42 provided on thearms 28A, 28B of the receiver member 14. In the illustrated embodiment,however, the closure mechanism 16 comprises an outer set screw 70positionable between and engaging the arms 28A, 28B of the receivermember 14 and an inner set screw 72 positionable within the outer setscrew 70. The outer set screw 70 is operable to act on the compressionmember 60 to fix the bone anchor 12 relative to the receiver member 14.The inner set screw 72 is operable to act on the spinal rod 22 to fixthe spinal rod 22 relative to the receiver member 14. In this manner,the closure mechanism 16 permits the bone anchor 12 to be fixed relativeto the receiver member 14 independently of the spinal rod 22 being fixedto the receiver member 14. In particular, the outer set screw 70 canengage the proximal end surfaces of the arms 62A, 62B of the compressionmember 60 to force the distal-facing surface 66 of the compressionmember 60 into contact with the proximal head 18 of bone anchor 12,which in turn forces the distal surface 38 of the proximal head 18 intofixed engagement with the distal inner surface of the receiver member14. The inner set screw 72 can engage the spinal rod 22 to force thespinal rod 22 into fixed engagement with the rod seat 64 of thecompression member 60.

The outer set screw 70 includes a first outer thread 74 for engaging acomplementary inner thread 42 on the arms 28A, 28B of the receivermember 14. The outer set screw 74 includes a central passage 96 from atop surface 98 of the outer set screw 74 to a bottom surface 100 of theouter set screw 74 for receiving the inner set screw 72. The centralpassage 96 can includes an inner thread 102 for engaging a complementaryouter thread 104 on the inner set screw 72. The thread form for theinner thread 102 and the outer thread 104, including the number ofthreads, the pitch, major and minor diameter, and thread shape, can beselected to facilitate connection between the components and transfer ofthe desired axial tightening force. The top surface 98 of the outer setscrew 74 can have one or more drive features to facilitate rotation andadvancement of the outer set screw 74 relative to the receiver member14. The illustrated outer set screw 74 includes drive features in theform of a plurality of cut-outs 106 spaced-apart about the perimeter ofthe top surface 98. The inner set screw 104 can include drive featuresfor receiving an instrument to rotate and advance the inner set screw 72relative to the outer set screw 74. The illustrated inner set screw 104includes drive features in the form of a central passage 108 having aplurality of spaced apart, longitudinally oriented cut-outs for engagingcomplementary features on an instrument.

The bone anchor assembly 10 can be used with a spinal fixation elementsuch as rigid spinal rod 22. The various components of the bone anchorassemblies disclosed herein, as well as the spinal rod 22, can beconstructed from various materials, including titanium, titanium alloys,stainless steel, cobalt chrome, PEEK, or other materials suitable forrigid fixation. In other embodiments, the spinal fixation element can bea dynamic stabilization member that allows controlled mobility betweenthe instrumented vertebrae.

In use, bone can be prepared to receive the bone anchor assembly 10,generally by drilling a hole in the bone which is sized appropriately toreceive the bone anchor 12. If not already completed, the bone anchorassembly 10 can be assembled, which can include assembling the boneanchor 12 and the receiver member 14, so that the distal shaft 20extends through the opening in the distal end 32 of the receiver member14 and the proximal head 18 of the bone anchor 12 is received in thedistal end 32 of the receiver member 14. A driver tool can be fittedwith the bone anchor 12 to drive the bone anchor 12 into the preparedhole in the bone. The compression member 60 can be positioned within thereceiver member 14 such that the arms 62A, 62B of the compression memberare aligned with the arms 28A, 28B of the receiver member 14 and thelower surface of the compression member 14 is in contact with theproximal head 18 of the bone anchor 12. A spinal fixation element, e.g.,the spinal rod 22, can be located in the recess 30 of the receivermember 14. The closure mechanism 16 can be engaged with the inner thread42 provided on the arms 28A, 28B of the receiver member 14. A torsionalforce can be applied to the outer set screw 70 to move it within therecess 30 using a tool which can engage the plurality of cut-outs 106 inthe upper facing surface of the outer set screw 70, so as to force thecompression member 60 onto the proximal head 18 of the bone anchor 12.Torsional forces can then be applied to the inner set screw 72 to moveit relative to the outer set screw 70 so that it contacts the spinal rod22 and can, for example, fix the spinal rod 22 relative to the receivermember 14 and the bone anchor 12.

One or more embodiments of inventive bone anchor assemblies aredescribed below.

Except as indicated below, the structure, operation, and use of theseembodiments is similar or identical to that of the bone anchor assembly10 described above. Accordingly, a detailed description of saidstructure, operation, and use is omitted here for the sake of brevity.FIGS. 3A-12 show various embodiments of rod-receiving recesses similarto the recesses formed by the receiver member 14 and/or the compressionmember 60 shown in FIG. 1B but with gripping recesses or features formedon the inner surface of the rod-receiving recess for gripping acylindrical rod 22 with greater friction as compared with the receivermember 14 and/or the compression member 60 of the bone anchor shown inFIG. 1B. The rod-receiving recesses shown in FIGS. 3A-12 can be usedwith the bone anchor assembly shown in FIGS. 1A-1D, or with variousother bone anchor assemblies known in the art. FIGS. 8C and 8D showrod-receiving recesses with locking members arranged to compress aninsert having gripping recesses or features formed therein against thecylindrical rod 22. The inserts shown in FIGS. 8C and 8D can be usedwith the bone anchor assembly shown in FIGS. 1A-1D, or with variousother bone anchor assemblies known in the art, and can be urged againstthe cylindrical rod 22 by a locking mechanism such as the outer setscrew 70 or inner set screw 72 shown in FIGS. 1A-1D.

FIGS. 2A-2L illustrate a prior art connector 200 with a traditionalconfiguration for securing a rod to the connector 200. As shown, theconnector 200 can include a body 202 that defines first and secondrod-receiving recesses 204, 206, a rod pusher 208, a bias element orspring wire 212, and a locking element or set screw 216. The rod pusher208 can be configured to translate laterally within the body 202, andcan be biased by the spring wire 212 in a direction that urges the rodpusher into a first rod R1 disposed in the first rod-receiving recess204. The set screw 216 can be tightened to lock the connector 200 toboth the first rod R1 and to a second rod R2 disposed in the secondrod-receiving recess 206. The illustrated connector 200 can thus allowfor one-step locking of first and second rods R1, R2 to the connector.The connector 200 can include one or more low-profile portions tofacilitate use in tight spaces. For example, the first rod-receivingrecess 204 can be formed in a portion of the connector body 202 having areduced-profile, e.g., to fit between bone anchors implanted in adjacentlevels of the cervical spine.

The body 202 can include proximal and distal ends 202 p, 202 d thatdefine a proximal-distal axis A1. The proximal end 202 p of the body 202can include a pair of spaced apart arms 218, 220 that define the secondrod-receiving recess 206 therebetween. A rod R2 disposed in the secondrod-receiving recess 206 can have a central longitudinal rod axis A2.The second rod-receiving recess 206 can be open in a proximal direction,such that a rod R2 can be inserted into the recess by moving the roddistally with respect to the connector 200. Each of the arms 218, 220can extend from the distal portion 202 d of the body 202 to a free end.The outer surfaces of each of the arms 218, 220 can include a feature(not shown), such as a recess, dimple, notch, projection, or the like,to facilitate coupling of the connector 200 to various instruments. Forexample, the outer surface of each arm 218, 220 can include an arcuategroove at the respective free end of the arms for attaching theconnector 200 to an extension tower or retractor. The arms 218, 220 caninclude or can be coupled to extension or reduction tabs (not shown)that extend proximally from the body 202 to functionally extend thelength of the arms 218, 220. The extension tabs can facilitate insertionand reduction of a rod or other implant, as well as insertion andlocking of the set screw 216. The extension tabs can be configured tobreak away or otherwise be separated from the arms 218, 220. The innersurfaces of each of the arms 218, 220 can be configured to mate with theset screw 216. For example, the inner surfaces of the arms 218, 220 caninclude threads that correspond to external threads formed on the setscrew 216. Accordingly, rotation of the set screw 216 with respect tothe body 202 about the axis A1 can be effective to translate the setscrew with respect to the body axially along the axis A1.

The distal end 202 d of the body 202 can define a tunnel 228 in whichthe rod pusher 208 can be disposed. The tunnel 228 can extend along arod pusher axis A3 between the second rod-receiving recess 206 and thefirst rod-receiving recess 204. The rod pusher 208 can be configured totranslate within the tunnel 228 along the axis A3. The axis A3 can beperpendicular or substantially perpendicular to the axis A1. The axis A3can also be perpendicular or substantially perpendicular to the axis A2.The tunnel 228 can have a shape that is substantially a negative of theexterior shape of the rod pusher 208. A through-bore 224 can be formedin the body 202 such that the through-bore intersects with the tunnel228. The through-bore 224 can extend perpendicular or substantiallyperpendicular to the axis A3. The through-bore 224 can be sized toreceive the spring wire 212 therein, as described further below. Thethrough-bore 224 can be open at both ends or one or both ends can beclosed.

The body 202 can include a cantilevered wing portion 230 that definesthe first rod-receiving recess 204. A rod R1 disposed in the firstrod-receiving recess 204 can have a central longitudinal rod axis A4.The axis A4 can be parallel to the axis A2 as shown, or can beperpendicular or obliquely angled with respect to the axis A2. The wingportion 230 can extend radially-outward from the second arm 220 of thebody 202. The wing portion 230 can have a width 230W and a height 230H.A ratio of the width 230W to the diameter of the first rod-receivingrecess 204 (or of a rod R1 disposed therein) can be less than about1.5:1, less than about 2:1, and/or less than about 3:1. A ratio of theheight 230H to the diameter of the first rod-receiving recess 204 (or ofa rod R1 disposed therein) can be less than about 0.5:1, less than about1:1, and/or less than about 2:1. The height 230H can be less than about5 mm, less than about 4 mm, and/or less than about 3 mm. The firstrod-receiving recess 204 can be open in a distal direction such that arod R1 can be inserted into the recess by moving the connector 200distally with respect to the rod. The first rod-receiving recess 204 canbe open in a proximal direction, e.g., by flipping the wing portion 230and forming it such that it extends from a distal portion of the body202, or in a lateral direction.

As noted above, the rod pusher 208 can be slidably disposed within thetunnel 228 of the body 202 and can be configured to translate withrespect to the body along the axis A3. The rod pusher 208 can include afirst bearing surface 244A configured to contact and bear against afirst rod R1 disposed in the first rod-receiving recess 204. The bearingsurface 244A can extend at an oblique angle with respect to alongitudinal axis of the rod pusher 208 such that the bearing surface isramped. The bearing surface 244A can be planar as shown, or can beconvex, concave, pointed, sharpened, etc. For example, the bearingsurface 244A can be concave and can define a section of a cylinder, suchthat the bearing surface matches or approximates the contour of acylindrical rod R1 disposed in the first rod-receiving recess 204. Therod pusher 208 can include a second bearing surface 244B configured tocontact and bear against a second rod R2 disposed in the secondrod-receiving recess 206. The bearing surface 244B can extend at anoblique angle with respect to a longitudinal axis of the rod pusher 208such that the bearing surface is ramped. The bearing surface 244B can beplanar as shown, or can be convex, concave, pointed, sharpened, etc. Forexample, the bearing surface 244B can be concave and can define asection of a cylinder, such that the bearing surface matches orapproximates the contour of a cylindrical rod R2 disposed in the secondrod-receiving recess 206.

The rod pusher 208 can include a through bore 226. The through-bore 226can extend perpendicular or substantially perpendicular to the axis A3.The through-bore 226 can be sized to receive the spring wire 212therein. In at least some positions of the rod pusher 208 with respectto the body 202, the through-bore 226 of the rod pusher can be alignedwith the through-bore 224 of the body, such that the spring wire 212extends through both through-bores 224, 226. As best shown in FIGS. 2D,2F, and 2H, the through-bore 226 can include a middle portion andopposed end portions. The middle portion of the through-bore 226 canapproximate the dimensions of the spring wire 212. For example, themiddle portion can be cylindrical and can have a diameter that issubstantially equal to the diameter of the spring wire 212. The endportions of the through-bore 226 can be elongated or can otherwise havea dimension greater than the diameter of the spring wire 212 to allowthe rod pusher 208 to translate along the axis A3 and to accommodate thebend radius of the spring wire 212 during such translation.

The bias element can be configured to bias the rod pusher 208 towardsthe first rod-receiving recess 204. In the illustrated view, the biaselement is a cylindrical spring wire 212. The spring wire 212 can beformed from a resilient material such that, when deformed from astraight line, the spring wire tends to flex back towards its straightresting configuration. Accordingly, when deformed by movement of the rodpusher 208, the spring wire 212 can exert a force against the interiorof the through-bore 226 to urge the rod pusher 208 towards the firstrod-receiving recess 204. While a straight, cylindrical spring wire 212is shown, various other bias elements can be used instead or inaddition, such as non-straight or non-cylindrical wires, leaf springs,spring clips, wave springs, coil springs, and the like. The bias elementcan be omitted. For example, the rod pusher 208 can be free to floatwithin the tunnel 228, or can be retained by a pin or other retentionfeature without being biased towards the first rod-receiving recess 204.

The set screw 216 can include an exterior thread configured to mate withthe interior threads formed on the arms 218, 220 of the body 202 toallow the set screw to be advanced or retracted along the axis A1 withrespect to the body by rotating the set screw about the axis A1. The setscrew 216 can include a driving interface 248 configured to receive adriver for applying a rotational force to the set screw about the axisA1. The distal surface of the set screw 216 can be configured to contactand bear against a rod R2 disposed in the second rod-receiving 206recess to lock the rod to the connector 200. When tightened against therod R2, the set screw 216 can prevent the rod from translating relativeto the connector 200 along the axis A2 and/or from rotating with respectto the connector about the axis A2. While a set screw 216 is shown, itwill be appreciated that other locking elements can be used instead oraddition, such as a closure cap that advances and locks by quarter-turnrotation, a closure cap that slides in laterally without rotating, a nutthat threads onto an exterior of the connector 200, and so forth.

Operation of the connector 200 is illustrated schematically in FIGS.2C-2H.

As shown in FIGS. 2C and 2D, the connector 200 can have a restingconfiguration in which no rod is disposed in the first or secondrod-receiving recesses 204, 206. In this configuration, the biasingforce of the spring wire 212 can cause the rod pusher 208 to slidetowards the first rod-receiving recess 204.

In the resting configuration, the wing portion 230 of the body 202 andthe free end of the rod pusher 208 can define an aperture 250 that issmaller than the diameter of a first rod R1 to which the connector 200is to be coupled. Accordingly, as shown in FIGS. 2E and 2F, as the rodR1 is inserted into the first rod-receiving recess 204, the rod bearsagainst the rod pusher 208 to move the connector 200 out of the restingconfiguration. Insertion of the rod R1 can move the rod pusher 208 alongthe axis A3, thereby deforming the spring wire 212 from its restingstate. As the largest cross-sectional portion of the rod R1 ispositioned in the aperture 250, the rod pusher 208 can be displaced toits furthest distance from the first rod-receiving recess 204.

As shown in FIGS. 2G and 2H, once the largest cross-sectional portion ofthe rod R1 clears the aperture 250 as the rod is seated in the firstrod-receiving recess 204, the biasing force of the spring wire 212 cancause the rod pusher 208 to move back along the axis A3 towards thefirst rod-receiving recess. This movement can at least partially closethe aperture 250 around the rod R1 to capture the rod in the firstrod-receiving recess 204. The biasing force of the spring wire 212 canresist retrograde movement of the rod pusher 208 and thus resistdisconnection of the connector 200 from the first rod R1. The geometryof the connector 200 can be selected such that, when the rod R1 is fullyseated in the first rod-receiving recess 204, the spring wire 212 isdeformed from its resting state. The spring wire 212 can thus press therod pusher 208 against the rod R1 to provide a friction or drag effect,before the set screw 216 is tightened and/or before a second rod R2 ispositioned in the connector 200.

A second rod R2 can be positioned in the second rod-receiving recess206, and the set screw 216 can be tightened to lock the connector 200 tothe first and second rods R1, R2. As the set screw 216 is tightened, thesecond rod R2 can press against the second bearing surface 244B of therod pusher 208, urging the rod pusher towards the first rod-receivingrecess 204 and firmly into contact with the rod R1. When the set screw216 is tightened, the connector 200 can be locked to the first andsecond rods R1, R2 to resist or prevent translation of the rods R1, R2with respect to the connector along the axes A2, A4 and to resist orprevent rotation of the rods R1, R2 with respect to the connector aboutthe axes A2, A4.

As shown in FIG. 2I, the second rod-receiving recess 206 can be shapedto encourage contact between the second rod R2 and the second bearingsurface 244B of the rod pusher 208. In other words, the recess 206 canbe shaped to reduce or eliminate the risk that the second rod R2 willonly bear against the floor of the recess 206 when the set screw 216 istightened, without applying sufficient force to the bearing surface244B. As shown, the recess 206 can include a relief disposed inalignment with the end of the tunnel 228 such that the rod pusher 208protrudes into the recess. The recess 206 can thus be asymmetrical aboutthe axis A1, and can deviate from a symmetrical U-shape. When the rod R2is bottomed out in the recess 206, the central longitudinal axis A2 ofthe rod can be offset from the axis A1. The central longitudinal axis ofthe rod R2 when the rod is fully seated is shown in FIG. 2I as axis A5.The recess 206 can be configured such that, as the rod R2 is seatedwithin the recess 206, it translates distally along the axis A1 andlaterally along the axis A3.

As shown in FIGS. 2J-2L, the connector 200 can include a saddle 210. Thesaddle 210 can be included in addition to the asymmetrical recess 206 oras an alternative thereto. The saddle 210 can be positioned within acavity 222 formed in the body 202. The saddle 210 can be generallycylindrical with first and second arms 232, 234 extending in a proximaldirection to respective free ends of the arms. The first and second arms232, 234 can be aligned with the first and second arms 218, 220 of thebody 202 such that a recess defined therebetween is aligned with thesecond rod-receiving recess 206. Accordingly, the second rod R2 can besimultaneously cradled between the arms 232, 234 of the saddle 210 andthe arms 218, 220 of the body 202 when the rod is disposed in the secondrod-receiving recess 206. The saddle 210 can include a ramped bearingsurface 240 configured to contact and bear against the second bearingsurface 244B of the rod pusher 208. The bearing surface 240 can extendat an oblique angle with respect to the axis A1. The bearing surface 240can be planar as shown, or can be convex, concave, pointed, sharpened,etc. In operation, a force applied to the saddle 210 along the directionA1, e.g., by tightening the set screw 216 down onto the saddle or downonto a rod R2 disposed in the saddle, can cause the saddle 210 totranslate distally with respect to the body 202 and cause the bearingsurface 240 to ramp along the bearing surface 244B of the rod pusher208, urging the rod pusher towards the first rod-receiving recess 204along the axis A3. Accordingly, tightening the set screw 216 can beeffective to simultaneously lock both rods R1, R2 to the connector 200.The saddle 210 can allow for locking of rods having different diametersin the second rod-receiving recess 206, while still ensuring that,regardless of the diameter of the second rod R2, sufficient force isapplied to the rod pusher 208 to lock the first rod R1.

Sometimes, the arms 232, 234 can extend proximally past the maximumdimension of the rod R2 and the set screw 216 can include an outer screwconfigured to bear against a proximal-facing surface of the arms. Aninner set screw can be threadably mounted within the outer set screw.Accordingly, the outer set screw can be tightened first to press down onthe saddle 210 and lock the first rod R1 in the first rod-receivingrecess 204. Then, the inner set screw can be tightened to press down onthe second rod R2 and lock the second rod in the second rod-receivingrecess 206. The dual set screw can thus facilitate independent lockingof the first and second rods R1, R2 to the connector 200. While notshown in FIGS. 2J-2L, connectors 200 that include a saddle 210 can alsoinclude a bias element as described above for biasing the rod pusher 208towards the first rod-receiving recess 204.

The connector 200 can thus be used to connect a first spinal rod R1 to asecond spinal rod R2. While use of the connector 200 with first andsecond spinal rods is generally described herein, it will be appreciatedthat the connector can instead be configured for use with other types oforthopedic hardware, whether implanted or external. For example, one orboth halves of the connector 200 can be modified to couple other variouscomponents to each other (e.g., to couple a rod to a plate, to couple aplate to a plate, to couple a rod to cable, to couple a cable to acable, and so forth).

The connector 200 can provide various benefits for the user and/orpatient. For example, the biased rod pusher 208 can provide tactilefeedback when the connector 200 is “snapped” onto the first rod R1,giving the user confidence that the rod has been attached successfullybefore tightening the connector. The biased rod pusher 208 can alsoapply friction or “drag” to the rod R1 prior to locking the set screw216, helping to keep the connector in place and prevent “flopping” whilestill allowing free movement when intended by the user. By way offurther example, the low-profile geometry of the wing portion 230 of theconnector 200 can allow the connector to be used in surgical areas wherespace is limited (e.g., in the cervical area of the spine). In anexemplary method, the wing portion 230 of the connector 200 can behooked onto a first rod R1 at a location between two bone anchors towhich the rod is coupled, the two bone anchors being implanted inadjacent vertebral levels of the cervical spine. As yet another example,the connector 200 can facilitate simultaneous and/or single-step lockingof the first and second rods R1, R2. This can allow the connector 200 tobe locked to both rods R1, R2 with minimal steps. In other instances,the connector 200 can facilitate independent locking of the rods R1, R2,e.g., with use of a saddle 210 and dual set screw.

Exemplary connector and implants are disclosed in U.S. PatentApplication Publication No. 2017/0333088, filed on Oct. 4, 2016, and inU.S. Patent Application Publication No. 2017/0333087, filed May 18,2016, both of which are incorporated herein by reference.

FIG. 3A is a cross-sectional view of a connector with a rod recesshaving two grip grooves. As shown, the connector 300 can include a body202 that defines first and second rod-receiving recesses 304, 306 and arod pusher 308. The rod pusher 308 can be configured to translatelaterally within the body 302, and can be biased in a direction thaturges the rod pusher 308 into a first rod R1 disposed in the firstrod-receiving recess 304. A set screw 216 can be tightened to lock theconnector 300 to both the first rod R1 and to a second rod R2 disposedin the second rod-receiving recess 306. The illustrated connector 300can thus allow for one-step locking of first and second rods R1, R2 tothe connector (as shown in FIGS. 2A-2L). The connector 300 can includeone or more low-profile portions to facilitate use in tight spaces. Forexample, the first rod-receiving recess 304 can be formed in a portionof the connector body 202 having a reduced-profile, e.g., to fit betweenbone anchors implanted in adjacent levels of the cervical spine.

The body 302 can include proximal and distal ends that define aproximal-distal axis A1, as shown in FIG. 2B. The proximal end of thebody 202 can include a pair of spaced apart arms 318, 320 that definethe second rod-receiving recess 306 therebetween. A rod R2 disposed inthe second rod-receiving recess 306 can have a central longitudinal rodaxis A2, as shown in FIG. 2B. The second rod-receiving recess 306 can beopen in a proximal direction, such that a rod R2 can be inserted intothe recess by moving the rod distally with respect to the connector 200.Each of the arms 318, 320 can extend from the distal portion of the body302 to a free end. The outer surfaces of each of the arms 318, 320 caninclude a feature (not shown), such as a recess, dimple, notch,projection, or the like, to facilitate coupling of the connector 300 tovarious instruments. For example, the outer surface of each arm 318, 320can include an arcuate groove at the respective free end of the arms forattaching the connector 300 to an extension tower or retractor. The arms318, 320 can include or can be coupled to extension or reduction tabs(not shown) that extend proximally from the body 302 to functionallyextend the length of the arms 218, 220. The extension tabs canfacilitate insertion and reduction of a rod or other implant, as well asinsertion and locking of the set screw 216, as shown in FIG. 2B. Theextension tabs can be configured to break away or otherwise be separatedfrom the arms 218, 220. The inner surfaces of each of the arms 318, 320can be configured to mate with the set screw 216. For example, the innersurfaces of the arms 318, 320 can include threads that correspond toexternal threads formed on the set screw 316. Accordingly, rotation ofthe set screw 316 with respect to the body 302 about the axis A1 can beeffective to translate the set screw with respect to the body axiallyalong the axis A1.

The body 302 can include a cantilevered wing portion 330 that definesthe first rod-receiving recess 304. As shown in FIG. 2B, a rod R1disposed in the first rod-receiving recess 304 can have a centrallongitudinal rod axis A4. The axis A4 can be parallel to the axis A2 asshown, or can be perpendicular or obliquely angled with respect to theaxis A2. The wing portion 330 can extend radially-outward from thesecond arm 320 of the body 302. The first rod-receiving recess 304 canbe open in a distal direction such that a rod R1 can be inserted intothe recess by moving the connector 300 distally with respect to the rod.The first rod-receiving recess 304 can be open in a proximal direction,e.g., by flipping the wing portion 330 and forming it such that itextends from a distal portion of the body 302, or in a lateraldirection.

The rod pusher 308 can be slidably disposed within the tunnel 328 of thebody 302 and can be configured to translate with respect to the bodyalong the axis A3, as shown in FIG. 2B. The rod pusher 308 can include afirst bearing surface 344A configured to contact and bear against afirst rod R1 disposed in the first rod-receiving recess 304. The bearingsurface 344A can extend at an oblique angle with respect to alongitudinal axis of the rod pusher 308 such that the bearing surface isramped. The bearing surface 344A can be planar as shown, or can beconvex, concave, pointed, sharpened, etc. For example, the bearingsurface 344A can be concave and can define a section of a cylinder, suchthat the bearing surface matches or approximates the contour of acylindrical rod R1 disposed in the first rod-receiving recess 204. Therod pusher 308 can include a second bearing surface 344B configured tocontact and bear against a second rod R2 disposed in the secondrod-receiving recess 306. The bearing surface 344B can extend at anoblique angle with respect to a longitudinal axis of the rod pusher 208such that the bearing surface is ramped. The bearing surface 344B can beplanar as shown, or can be convex, concave, pointed, sharpened, etc. Forexample, the bearing surface 344B can be concave and can define asection of a cylinder, such that the bearing surface matches orapproximates the contour of a cylindrical rod R2 disposed in the secondrod-receiving recess 306.

FIG. 3A shows the first rod-receiving recess 304 including two gripgrooves 301 opposite to the bearing surface 344A. The grip grooves 301are formed as recesses in the inner surface of the first rod-receivingrecess 304, as shown more clearly in FIG. 3B.

FIG. 3B is a cross-sectional view of the rod-receiving recess 304 of theconnector of FIG. 3A. FIG. 3B shows that the grip grooves 301 eachdefine two edges 312, 313, 322, 323 that are configured to contact thesurface of the cylindrical rod R1 disposed in the first rod-receivingrecess 304. The grip grooves 301 extend along the axis A4 and the firstrod-receiving recess 304 is sized and shaped such that the side of thecylindrical rod R1 that faces the grip grooves 301 is urged into contactagainst the edges 312, 313, 322, 323 by the rod pusher 308, such thatadditional force applied to the cylindrical rod R1 by the rod pusher 308further engages the cylindrical rod R1 against the edges 312, 313, 322,323. This can be accomplished by, for example, having the inner surfaceof the rod-receiving recess 304 and the location of the grip grooves 301sized and shaped such that the edges 312, 313, 322, 323 define a radiusabout the axis A4 that approximately matches the radius of thecylindrical rod R1 and, when the cylindrical rod R1 is urged into therod-receiving recess 304, the half of the cylindrical rod R1 oppositethe first bearing surface 344A of the rod pusher contacts therod-receiving recess 304 only at engages the edges 312, 313, as shown inmore detail in FIG. 3C.

FIG. 3C is a cross-sectional view of the grip grooves 301 of therod-receiving recess 304 of the connector 300 of FIG. 3A. FIG. 3C showsthe cylindrical rod R1 (solid line) disposed in the rod-receiving recess304 and in contact with the edges 312, 313, such that a small portion ofthe outer surface of the cylindrical rod R1 is received inside each gripgroove 301. This illustrated configuration shows that the cylindricalrod R1 makes contact with the rod-receiving recess 304 along 4 points ofcontact, in contrast with the prior art rod-receiving recess 204 withoutgrip grooves. This prior art configuration is shown in FIG. 3C as theposition of a cylindrical rod R1′ is overlaid the cylindrical rod R1.The position of a cylindrical rod R1′ (dotted line) corresponds toposition the cylindrical rod R1′ in the rod-receiving recess 304 withoutgrip grooves 301 as shown more clearly in FIG. 4A. FIG. 3C shows theradius 398 of the cylindrical rod R1 and the distance 399 of each edge312, 313 from the central longitudinal axis A4 of the rod-receivingrecess 304 are approximately the same.

FIG. 4A is a cross-sectional view of a prior art rod-receiving recess.FIG. 4A shows a cylindrical rod R1 disposed in a prior art rod-receivingrecess 204 without grip grooves. In this configuration, the cylindricalrod R1 contacts the inner surface of the rod-receiving recess 204 at twopoints P1, P2. In operation, these two points P1, P2 can define parallellines of contact along the axis A4 (e.g., along the surface of thecylindrical rod R1 that contacts the inner surface of the rod-receivingrecess 204). The particular interface of the cylindrical rod R1 and therod-receiving recess 204 at these points P1, P2 is a curved surface(e.g., the cylindrical rod R1) against a flat or angled surface (e.g.,the rod-receiving recess 204). With this engagement, both the rotationof the cylindrical rod R1 about axis A4 and translation of thecylindrical rod R1 in the A4 direction are restrained by the forceapplied by surface of the rod-receiving recess 204 against thecylindrical rod R1, which depends on the force applied by the rod pusher208 and the friction forces between the cylindrical rod R1 and thesurface of the rod-receiving recess 204. The radius 498 of thecylindrical rod R1 is shown with respect to the central axis R of thecylindrical rod R1.

As illustrated in FIG. 4B, aspects of the present disclosure provideimproved retaining of the cylindrical rod R1 in a rod-receiving recess304. FIG. 4B is a cross-sectional view of a rod-receiving recess 308having v-shaped grip grooves 401. The-shaped grip grooves 401 defineedges 412, 413 that are positioned to be contacted by the surface of thecylindrical rod R1 at points E1-E4. That is, the v-shaped grip grooves401 are formed in the surface of the rod-receiving recess 304 such thatthe edges 412, 413 define four points on a circle with a radiusapproximately the same as the cylindrical rod R1. In operation, thecylindrical rod R1 rests against the four edges 412, 413 and rod pusher308 applies a force 488 to the cylindrical rod R1 that urges the surfaceof the cylindrical rod R1 against the edges 412, 413. In contrast to theprior art surface-to-surface engagement of FIG. 4A, the curved surfaceof the cylindrical rod R1 is pressed against sharp edges 412, 413 (e.g.,corners or apexes creating an edge of a sufficiently small radius orthickness to be able to be deformed by the cylindrical rod R1 or todeform the surface of the cylindrical rod R1 to allow the cylindricalrod R1 to be urged into the grip grooves 401), such that rotation of thecylindrical rod R1 while pressed against the four edges 412, 413requires micro shearing of the edges 412, 413 at the points of contactE1-E4. Accordingly, the grip grooves 401 constrain the rotation of thecylindrical rod R1 in the rod-receiving recess 304 in a manner thatrequires material property failure to allow movement between the edges412, 413 and the cylindrical rod R1. As a result, for an equal forceapplied to the cylindrical rod R1 by the rod pusher 308, the gripgrooves 401 are able to withstand higher torque on the cylindrical rodR1 about axis A4 before movement occurs.

In some instances, in order to ensure the engagement between thecylindrical rod R1 and the edges 412, 413, a pocket 450 is formed in therod receiving recess 304, such that the movement of the cylindrical rodR1 against the edges 412, 413 as driven by the rod pusher 308 is notinterrupted by the cylindrical rod R1 contacting the inner surface ofthe rod receiving recess 308. This configuration can allow the initialurging of the cylindrical rod R1 against the edges 412, 413 to createsome deformation at the points of contact E1-E4 (e.g., deformation ofeither of the material of the cylindrical rod R1, the edges 412, 413, orboth), such that any initial rotation of the cylindrical rod R1 inducesfurther material deformation at the points of contact E1-E4.

While FIG. 4B shows the body 302 having two grip grooves 401, in someinstances, the body 302 has only one grip groove 401, for example, withthe single grip groove 401 located opposite the clamping force vector,such that the force vector 488 and the center of the grip groove 401intersects the central axis A4 of the rod R1.

FIG. 4B also shows the radius 498 of the cylindrical rod R1 and thedistance 499 of each edge 412, 413 from the central longitudinal axis A4of the rod-receiving recess 304 can be approximately the same to allowthe surface of the cylindrical rod R1 to evenly contact the edges 412,413, in which case the central axis R of the cylindrical rod R1 isconcentric with the central longitudinal axis A4 of the rod-receivingrecess 304.

FIG. 4C is a cross-sectional view of the rod-receiving recess 304 ofFIG. 4B showing a comparison of the position of a cylindrical rod R1with and without the grip grooves 401. FIG. 4C shows both the positionof cylindrical rod R1 engaged with the grip grooves 401 as shown in FIG.4B, as well as the same cylindrical rod R1 positioned in therod-receiving recess 204 without the grip grooves 401 (as shown bydotted line R1′). Compared with the position of the cylindrical rod R1′against the rod-receiving recess 204, the cylindrical rod R1 in therod-receiving recess 304 having the grip grooves 401 is positionedfarther into the pocket 450 because a small portion of the surface ofthe cylindrical rod R1 is received into the grip grooves 401 to allowthe edges 412, 413 to all contact the surface of the cylindrical rod R1.

FIG. 4D is a perspective view of a cylindrical rod R1 showing lines ofcontact E1-E4 made by the edges 412, 413 of the two grip grooves 401when the cylindrical rod R1 is positioned in a rod-receiving recess 304(as shown in FIG. 4B). FIG. 4D shows the resultant contact between arod-receiving recess 304 with grip grooves 401 that span the length ofthe cylindrical rod R1. This allows the cylindrical rod R1 to be pressedinto the edges 412, 413 along the lines of contact E1-E4 such that theforce applied to the cylindrical rod R1 is not disrupted by contactbetween the cylindrical rod R1 and the rod-receiving recess 304 exceptfor along the lines of contact E1-E4. In some instances, and asexplained in more detail below, additional points and lines of contactbetween the cylindrical rod R1 and the rod-receiving recess 304 arewithin the scope of this disclosure, however, such additional contactsstill permit a sufficient portion of the force applied to cylindricalrod R1 to be directed against the edges 412, 413 along the lines ofcontact E1-E4 in order to create the condition whereby rotation of thecylindrical rod R1 is resisted by a requirement for material deformationof one or both of the cylindrical rod R1 and the edges 412, 413 alongthe lines of contact E1-E4. FIG. 4D shows that the lines of contactE1-E4 are oriented to resist rotation of the cylindrical rod R1 in boththe clockwise CW and counterclockwise CCW directions.

FIG. 4E is a perspective view of a surface 410 of a rod-receiving recess304 with a segmented grip groove 403. The segmented grip groove 403 isformed when a grip groove 401 is intersected by one or more recesses orgrooves 408. FIG. 4E shows the segmented grip groove 403 formed by agrip groove 401 that is intersected by two recesses 408 oriented atright angles to the grip groove 401. In some embodiments, however, otherangles are possible such that the one or more recesses or grooves 408are transverse to the grip groove 401 (e.g., oblique to, etc.). Theintersection of the grip groove 401 by the grooves 408 creates breaks inthe grip groove edges 412, 413 along the length of the cylindrical rodR1, as shown in FIG. 4F, which are now referred to as segmented edges412, 413.

FIG. 4F is a top-down view of the segmented grip groove of FIG. 4E. Inoperation, the segmented edges 412, 413 serve to constrain movement ofthe cylindrical rod R1 along the length of the segmented grip groove 403(i.e., translation along axis A4) by creating point edges 480 (e.g.,small corners as the rod is urged into the groove and each point edge480 forms a small corner of contact with the rod R1), as shown in FIG.4G that engage the surface of the cylindrical rod R1 and enable thesegmented edges 412, 413 to apply a force on the cylindrical rod R1 inthe A4 direction. FIG. 4G is a schematic illustration of the contactpoints F1-F4 on the cylindrical rod R1 engaged with the segmented gripgroove 403 of FIG. 4E. FIG. 4G shows that when the cylindrical rod R1 ispressed into engagement with the segmented grip groove 403, theresulting contact lines F1, F2 of the segmented edges 412, 413 aresegmented as well. With the cylindrical rod R1 engaged with thesegmented edges 412, 413, the point edges or small corners 480 definethe transition between a point on the cylindrical rod R1 where thesegmented edges 412, 413 are and are not contacting the cylindrical rodR1. If, for example, the material properties of the cylindrical rod R1and the segmented edges 412, 413 are chosen such that the surface of thecylindrical rod R1 is deformed when in contact with the segmented edges412, 413, then the point edges 480 together resist translation of therod along the segmented grip groove 403 (i.e., translation along axisA4) by virtue of this movement resulting in two of the four illustratedpoint edges 480 being driven into an un-deformed region of the surfaceof the cylindrical rod R1. Therefore, the segmented grip groove 403 canresist both rotation and translation of the cylindrical rod R1 in therod-receiving recess 403, as shown in FIG. 4F.

FIG. 4H is a perspective of a surface of a cylindrical rod R1 showingsegmented lines of contact F1-F4 made by the edges of two segmented gripgrooves 403 when the cylindrical rod R1 is positioned in therod-receiving recess 304. Clockwise CW and counterclockwise CCW rotationof the cylindrical rod R1 is resisted by the segmented grip grooves 403in the same manner as described above with respect to non-segmented gripgrooves 401, and translation of the cylindrical rod R1 is resisted bythe point edges 480 created between the segmented edges 412, 413

While FIG. 3A shows grip grooves 301 having a cylindrical shape and FIG.4B shows grip grooves 401 having a V-shape, other shapes are possible.For example, FIG. 5A is a cross-sectional view of a rod-receiving recess403 having grip grooves 501 of a rectangular shape, where the edges 512,513 are right angles. FIGS. 3A-5A show the grip grooves 301, 401, 501 asrecesses formed on the inner surface of the rod-receiving recess 304,but the grip grooves can also be formed by protrusions 540 extendingfrom the inner surface of the rod-receiving recess 304, as shown in FIG.5B.

FIGS. 3A-5B show the grip grooves 301, 401, 501 formed on wing portion330 of the body 302 with the rod pusher 308 arranged to apply a force tothe cylindrical rod R1 to drive the cylindrical rod R1 against the gripgrooves 301, 401, 501, but other configurations are possible. Forexample, FIG. 6A is a cross-sectional view of a rod-receiving recess 304with the rod pusher 308 having grip grooves 601. As shown, the gripgrooves 601 define edges 612, 613 that contact the cylindrical rod R1 atfour contact points E1-E4 that define a circle of approximately the sameradius as the cylindrical rod R1. In FIG. 6A, the surface of therod-receiving recess opposite the rod pusher 308 defines a curvedsurface 651 that contacts the cylindrical rod R1 to apply a force thatopposes the force applied to the cylindrical rod R1 by the edges 612,613 of the grip grooves 601 of rod pusher 308. In operation, the gripgrooves 601 of the rod pusher 308 function in the same manner as thegrip grooves 301, 401, 501 described above. FIG. 6B is a cross-sectionalview of a rod-receiving recess 304 with a pocket 450 and a rod pusher308 having grip grooves 601. FIG. 6C shows both the rod-receiving recess304, grip grooves 501, and the rod pusher 308 having grip grooves 601.In this configuration, the position of the cylindrical rod R1 is highlyconstrained by the grip grooves 501, 601 as the eight points of contactE1-E8 all engage with the surface of the cylindrical rod R1. However, insome instances, the tolerances in the positions of the eight points ofcontact E1-E8 is reduced upon initial contact with the cylindrical rodR1 such that the cylindrical rod R1 is highly constrained oncesufficient force is applied to sufficiently engage the cylindrical rodR1 about the eight points of contact E1-E8.

FIG. 7A is a cross-sectional view of a single grip groove 501 having aninternal protrusion 710 arranged to contact the surface of thecylindrical rod R1 between the edges 512, 513 of the grip groove 501. Inorder to increase the restraint of the cylindrical rod R1 in thetranslational direction (i.e., along axis A4), additional grip featurescan be included inside the grip groove 501 in order to providetranslational restraint with a minimal to negligible effect on therotational restraint provided by the edges 512, 513. In FIG. 7A the gripgroove 501 includes one or more protrusions 701 along the length of thegrip groove 501. The internal protrusions 710 extend towards thecylindrical rod R1 and include a feature, such as end edge 711 that ispositioned to contact the cylindrical rod R1 when the cylindrical rod R1is engaged with the edges 512, 513 of the grip groove 501. FIG. 7A showsan internal protrusion 710 with an edge 711 contacting the cylindricalrod R1 along a line of contact L1 that is perpendicular to the lines ofcontact E1, E1 created by the edges 512, 513. In operation, the positionand shape of the edge 711 in the grip groove 501 can be configured tovary the strength of the contact line L1 between the cylindrical rod R1and the edge 711 when the cylindrical rod R1 is in contact with theedges 512, 513, as shown in more detail in FIGS. 7D and 7E.

FIG. 7B is a top-down view of the grip groove 501 of FIG. 7A showing theperpendicular edges 711 of two internal protrusions 710 creating twoparallel lines of contact L1, L2 on the cylindrical rod R1. FIG. 7C is across-sectional view of the grip groove 501 of FIG. 7A showing the edges711 of the internal protrusions 710 contacting the cylindrical rod R1when the rod is engaged with the grip groove 501.

FIG. 7D is a perspective view of a cylindrical rod R1 showing lines ofcontact E1-E4 made by the edges 512, 513 of two grip grooves 501 and thelines of contact L1-L4 made by two internal protrusions 710 in each gripgroove 501. In operation, the lines of contact E1-E4 made by the edges512, 513 resist rotation of the cylindrical rod R1 in the clockwise CWand counterclockwise CCW directions, and the lines of contact L1-L4 madeby two internal protrusions 710 resist translation of the cylindricalrod R1 in the A4 direction.

FIGS. 7E and 7F are cross-sectional views of a single grip groove 501having an internal protrusion 710 with two different edgeconfigurations. In a first configuration, shown in FIG. 7E, the internalprotrusion 710 extends to a flat edge 711 that will define a line ofcontact L1 with the cylindrical rod R1 that lengthens as the cylindricalrod R1 is urged against the edges 512, 513. Because the initial size ofthe line of contact L1 is small, the resistance to movement of thecylindrical rod R1 into the grip groove 510 is minimal, ensuring that apositive engagement between the cylindrical rod R1 and the internalprotrusion 710 is established. In a second configuration, shown in FIG.7F, the internal protrusion 710 has a curved edge 712 that is shaped toinitially contact the cylindrical rod R1 with a longer line of contactL1, in order to increase the translational restraint of the cylindricalrod R1 upon initial contact with the edges 512, 513. The resultantstrength of the restraint of the two different edge shapes 711, 712 candepend on the material properties of the cylindrical rod R1, edges 512,513, and internal protrusion 710 and the location of the edge 711, 712with respect to the edges 512, 513. For example, if the cylindrical rodR1 is made from a metal that is softer than the metal of the internalprotrusion 710, then the edge 711, 712 can extend closer to the radiusof the edges 512, 513 (i.e., the expected location of the cylindricalrod R1), such that the cylindrical rod R1 first contacts the edge 711,712 and the edge 711, 712 is driven into the surface of the cylindricalrod R1 as the cylindrical rod R1 interfaces with the edges 512, 513.

FIG. 8A is a cross-sectional view of a prior art rod-receiving recess206 of, for example, a receiver member 14 of a bone anchor assembly 10or a body 202 of a connector 200. A cylindrical rod R1 is disposed inthe rod-receiving recess 206 and contacts the inner surface of therod-receiving recess 206 at two points P1, P2 along the axis of therod-receiving recess 206. A locking element or set screw 104, 216contacts the cylindrical rod R1 at point P3 and applies force to urgethe cylindrical rod R1 into the rod-receiving recess 206 and against thetwo points P1, P2.

FIG. 8B is a cross-sectional view of a rod-receiving recess 306 with twogrip grooves 801 formed as parallel recesses in the inner surface of therod-receiving recess 306. FIG. 8B shows a cylindrical rod R1 disposed inthe rod-receiving recess 306 and engaged with the edges 812, 813 of thegrip grooves 801. A threaded locking element or set screw 104, 216 isarranged to secure the cylindrical rod R1 in the rod-receiving recess306 by applying a force to the cylindrical rod R1 to urge thecylindrical rod R1 against the edges 812, 813 of the grip grooves 801.FIG. 8B also illustrates the position of the cylindrical rod R1 would bein the rod-receiving recess 306 if the grip grooves 801 were missing,which is shown as R1′. The difference between R1′ and the position ofthe cylindrical rod R1 with the grip grooves 801 is due to the gripgrooves 801 defining edges 812, 813 along the inner surface of therod-receiving recess 306 at four locations with approximately the sameradius from an central axis of the rod-receiving recess 306 as thecylindrical rod R1, which thereby permits the central axis of thecylindrical rod R1 to be concentric with the axis defined by the equalradius location of the edges 812, 813. Said otherwise, the grip grooves801 are positioned to allow the cylindrical rod R1 to rest against all 4edges 812, 813 when urged into the rod-receiving recess 306 by thelocking element or set screw 104, 216. In some instances, therod-receiving recess 306 defines a pocket or gap 850 below the designedposition of the cylindrical rod R1 (as determined by the grip grooves801), in order to allow additional urging of the cylindrical rod R1 intothe rod-receiving recess 306 by the set screw 104, 216 to result inincreased pressure on the edges 812, 813.

FIGS. 8C and 8D illustrate embodiments where the grip grooves 801 arepositioned on an insert 816 that is driven against the cylindrical rodR1 in the rod-receiving recess 306. The insert 816 is driven by setscrew 104, 216 against the cylindrical rod R1, but does not rotate withthe set screw 104, 216 because the insert 816 is shaped to extend thegrip grooves 801 along a length of the cylindrical rod R1. The insert816 can include a peg 817 to be received by the set screw 104, 216 inorder to couple the grooves 801 with the body 302 (into which the setscrew 104, 216 is threaded, not shown) to allow the body 302 to opposerotation of the cylindrical rod R1 via the cylindrical rod's R1engagement with the grip grooves 801. FIG. 8C shows the rod-receivingrecess 306 having a circular section to provide surface contact with thecylindrical rod R1 to oppose the force of the insert 816, and FIG. 8Dshows the rod-receiving recess 306 having a tapered closed end with agap 850 providing two lines of contact P1, P2 with the cylindrical rodR1 to oppose the force of the insert 816.

FIG. 9 is a perspective view of a receiving member 902 having arod-receiving recess 904 with two grip grooves 801 formed therein. FIG.10 is a perspective view of a receiving member 902 having arod-receiving recess 904 with two circumferential grooves 1020 cut intothe rod-receiving recess 904 perpendicular to the central longitudinalaxis of the receiving recess 904.

FIGS. 11A and 11B are perspective views of a receiving member 902 havinga rod-receiving recess 904 with two segmented grip grooves 403 formedtherein by the intersection of two grip grooves 801 and twocircumferential grooves 1020. FIG. 11B shows the point edges 480 createdin by the segmented grip grooves 403. FIG. 12 is a perspective view of areceiving member 902 having a rod-receiving recess 906 with a gripgroove 801 having multiple internal protrusions 710 formed therein. Thereceiving member 902 and rod-receiving recess 904 of FIGS. 9-11B couldbe a body 302 of a connector 300, for example, or a receiver member 14of a bone anchor assembly 10, or any other implant configured to besecured to a rod, cable, or other spinal fixation element.

FIG. 13 is an illustration of a connector 300 with a saddle 301 thatdefines a rod-receiving recess with grip grooves 1301. In the connector300 of FIG. 13, the cylindrical rod R1 is secured to the receivingmember 14 by being engaged with a rod-receiving recess formed by aninner surface the saddle 301, and the inner surface of the saddle 60includes two grip grooves 1301 configured to grip the cylindrical rod R1when the locking screw 216 applies a force on the cylindrical rod R1 tourge the cylindrical rod R1 into the grip grooves 1301.

FIG. 14 is an illustration of a bone anchor assembly 10 with acompression member 60 that defines a rod-receiving recess with gripgrooves 1401. In the bone anchor assembly of FIG. 14, the cylindricalrod R1 is secured to the receiver member 14 by way of contact with acompression member 60 disposed in the receiver member, where an innersurface of the compression member 60 that forms the rod-receiving recessincludes the grip grooves 1401 that contact the cylindrical R1. Inoperation, the inner set screw 102 applies a force to the cylindricalrod R1 to urge that cylindrical rod R1 into the grip grooves 1401.

FIG. 15 is a perspective view of a human spine with a fixation systemattached thereto.

An exemplary method of using the bone anchors and connectors disclosedherein is described below. In some instances, the bone anchors andconnectors are each secured to one or two rods in order to, for example,bridge between constructs in the cervical and thoracic regions of apatient's spine. The bone anchors and connectors can be secured to therods using rod-receiving recesses with grip grooves in order to increaseresistance to movement of the rods, connectors, ad bone anchors,relative to one another.

The procedure can begin by forming an open or percutaneous incision inthe patient to access a target site. The target site can be one or morevertebrae, a long bone or multiple portions of a long bone, or any otherbone or non-bone structure of the patient. As shown in FIG. 15, thetarget site can be multiple vertebrae in the patient's cervical andthoracic spine.

Bone anchors can be driven into one or more of the vertebrae and spinalrods can be attached thereto using known techniques. In the illustratedexample, bilateral spinal rods R1, R2 are coupled to four adjacentvertebrae V1-V4 using eight bone anchors S1-S8. In addition, bilateralrods R3, R4 are coupled to the next two adjacent vertebrae V5-V6 usingfour bone anchors S9-S12. The rods R1, R2 can be connected to the rodsR3, R4, respectively, using four connectors C1-C4 of the type describedherein (e.g., connector 300) and the bone anchors S1-S8 can be connectedto the rods R1-R4 using receivers of the type described herein (e.g.,receiver 902).

As shown, the low-profile nature of the connectors C1-C4 can allow themto be installed at adjacent vertebral levels on the same rod (e.g.,between V2/V3 and between V3/V4). As also shown, the connectors C1-C4can connect to the rods R1, R2 between bone anchors installed inadjacent vertebral levels.

The connectors C1-C4 can receive the rods in respective rod-receivingrecesses, with the rod-receiving recesses having grip grooves to securethe connector to the rods R1, R2, thereby providing improved rotationaland, in some instances, axial restraint of motion of the rods R1, R2relative to the connectors.

The connectors C1-C4 can include independent locking features such thatthey can be locked to the rods R1, R2 prior to being locked to the rodsR3, R4 or vice versa.

The connectors C1-C4 can include single-step locking features such thatthey can be simultaneously locked to their respective rods. For example,connector C1 can be simultaneously locked to rods R1 and R3.

All of the rods R1-R4, the connectors C1-C4, and the bone anchors S1-S12can be installed in a single procedure.

Alternatively, the rods R1, R2 and the bone anchors S1-S8 may have beeninstalled in a previous procedure, and the current procedure can be arevision procedure in which the rods R3, R4, the connectors C1-C4, andthe bone anchors S9-S12 are installed to extend the previously-installedconstruct to additional levels.

The connectors C1-C4 can be attached to position the rods R1-R4 suchthat they are substantially parallel to one another and substantiallylie in a common coronal plane as shown. The connectors C1-C4 can also berotated 90 degrees from the orientation shown to position the rod pairsR1, R3 and R2, R4 such that they substantially lie in respective commonsagittal planes.

The above steps can be repeated to install additional rods and/orconnectors at the same or at different vertebral levels. Finaltightening or other adjustment of the construct can be performed and theprocedure can be completed using known techniques and the incisionclosed.

It should be noted that any ordering of method steps expressed orimplied in the description above or in the accompanying drawings is notto be construed as limiting the disclosed methods to performing thesteps in that order. Rather, the various steps of each of the methodsdisclosed herein can be performed in any of a variety of sequences. Inaddition, as the described methods are merely exemplary embodiments,various other methods that include additional steps or include fewersteps are also within the scope of the present disclosure.

While the methods illustrated and described herein generally involveattaching spinal rods to multiple vertebrae, it will be appreciated thatthe connectors and methods herein can be used with various other typesof fixation or stabilization hardware, in any bone, in non-bone tissue,or in non-living or non-tissue objects. The connectors disclosed hereincan be fully implanted, or can be used as part of an external fixationor stabilization system. The devices and methods disclosed herein can beused in minimally-invasive surgery and/or open surgery.

The devices disclosed herein and the various component parts thereof canbe constructed from any of a variety of known materials. Exemplarymaterials include those which are suitable for use in surgicalapplications, including metals such as stainless steel, titanium, oralloys thereof, polymers such as PEEK, ceramics, carbon fiber, and soforth. The various components of the devices disclosed herein can berigid or flexible. One or more components or portions of the device canbe formed from a radiopaque material to facilitate visualization underfluoroscopy and other imaging techniques, or from a radiolucent materialso as not to interfere with visualization of other structures. Exemplaryradiolucent materials include carbon fiber and high-strength polymers.

Although specific embodiments are described above, it should beunderstood that numerous changes may be made within the spirit and scopeof the concepts described.

1. An implant, comprising: a body having a rod-receiving recess, thebody having first and second sides defining openings to therod-receiving recess, the rod-receiving recess defining a centrallongitudinal rod axis extending between the openings of the first andsecond sides, wherein at least a portion of the rod-receiving recess isformed by an inner surface of the implant, the inner surface definingtwo grip grooves extending parallel to each other and the centrallongitudinal rod axis, wherein each grip groove defines two edges wherethe grip groove intersects the inner surface, the four edges of the twogrip grooves together defining a circular radius about the centrallongitudinal rod axis; and a retaining member configured to move withrespect to the body, exert a force against a rod in the rod-receivingrecess that is perpendicular to the central longitudinal rod axis, andengage the rod against the four edges of the two grip grooves, whereinthe engagement of the four edges of the grip grooves against the rodserves to restrain rotational movement of the rod about the centrallongitudinal rod axis.
 2. The implant of claim 1, wherein therod-receiving recess defines a gap between the two grip grooves sizedand positioned to allow the force against the rod in the rod-receivingrecess to permit deflection of one or both of the edges and the rodwhere the edges engage the rod, the deflection causing movement of therod into the gap.
 3. The implant of claim 2, wherein the inner surfaceof the rod-receiving recess between the two grip grooves is positioned adistance away from the central longitudinal rod axis that is larger thana radius of the rod.
 4. The implant of claim 1, comprising a compressionmember disposed in a cavity formed in the body, the compression memberhaving an inner surface defining at least a portion of the rod-receivingrecess, an inner surface of the compression member having the two gripgrooves formed therein.
 5. The implant of claim 1, wherein the gripgrooves extend along an entire length of the inner surface of therod-receiving recess in the direction of the central longitudinal rodaxis.
 6. The implant of claim 1, wherein the grip grooves are positionedopposite the retaining member with respect to the central longitudinalrod axis.
 7. The implant of claim 1, wherein the rod-receiving recessdefines an open end sized to accept the rod and a closed end sized tocontact the rod, wherein the grip grooves are arranged symmetricallyabout an axis extending from the open end to the closed end.
 8. Theimplant of claim 1, wherein the body of the implant defines the innersurface forming the rod-receiving recess.
 9. The implant of claim 1,wherein the intersection between the grip grooves and the inner surfacedefines sharp edges.
 10. The implant of claim 1, wherein the innersurface defines a groove intersecting at least one grip groove, theintersection of the groove segmenting the edges of the at least one gripgroove and defining four corners for resisting translation of the rodalong the central longitudinal rod axis when the rod is engaged with theedges.
 11. The implant of claim 9, wherein, the groove intersecting atleast one grip groove is oriented perpendicular to the grip grooves. 12.The implant of claim 1, wherein at least one grip grooves defines aninner surface having formed therein one or more protrusions, the one ormore protrusions extending to edges arranged to contact the rod when therod is engaged with the edges of the grip grooves.
 13. The implant ofclaim 1, wherein the grip grooves are formed by protrusions extendingfrom the inner surface.
 14. The implant of claim 1, wherein the implantcomprises a connector and the rod-receiving recess is a firstrod-receiving recces, the body defining a second rod-receiving recesswith one or both of the first and second rod-receiving recesses havingthe two grip grooves, the body having proximal and distal ends thatdefine a proximal-distal axis extending therebetween; wherein theretaining member is slidably disposed within a tunnel formed in the bodyand configured to translate with respect to the body along a rod pusheraxis.
 15. The implant of claim 14, wherein the second rod-receivingrecess is defined by a pair of spaced apart arms of the body.
 16. Theconnector of claim 14, wherein the first rod-receiving recess is open ina distal direction and wherein the second rod-receiving recess is openin a proximal direction.
 17. The connector of claim 14, wherein the rodpusher axis is substantially perpendicular to the proximal-distal axis.18. The connector of claim 14, further comprising a set screw threadablyreceived in the body to lock a first rod within the first rod-receivingrecess and to lock a second rod within the second rod-receiving recess.19. The implant of claim 1, wherein the implant comprises a bone anchorassembly, the body comprises a receiver member of the bone anchorassembly, and the retaining member comprises a set screw or lockingelement.
 20. An implant, comprising: a body having a rod-receivingrecess, the body having first and second sides defining openings to therod-receiving recess, the rod-receiving recess defining a centrallongitudinal rod axis extending between the openings of the first andsecond sides; a grip insert configured to be positioned in an open endof the receiving recess and defining an inner surface for contacting arod disposed in the rod-receiving recess, the inner surface defining twogrip grooves extending parallel to each other and the centrallongitudinal rod axis, wherein each grip groove defines two edges wherethe grip groove intersects the inner surface, the four edges of the twogrip grooves together defining a circular radius about the centrallongitudinal rod axis; and a retaining member configured to move withrespect to the body, exert a force against a rod in the rod-receivingrecess, and engage the four edges of the grip against the rod, whereinthe engagement of the four edges of the grip grooves against the rodserves to restrain rotational movement of the rod about the centrallongitudinal rod axis.